MILLIONS of households who are ­facing crippling rises in their monthly energy charges will be hit by further big price hikes by the end of the year, experts warned last night.

The harsh winter, extending into a cold spring, plus price rises expected in the autumn could push the average annual dual fuel bill up by 10 per cent to £1,600.

The warning comes as the energy giants write to customers who pay by direct debit to tell them they face big increases in their monthly payments to recoup costs for “exceptional” use over the past few months.

Mark Todd, the founder of energyhelpline.com, hit out at the “cruel reality that customers are paying more and more as the companies make more profits”.

He said industry rumours suggest the big six suppliers – E.ON, British Gas, EDF Energy, npower, Scottish Power and SSE – will increase prices by five to 10 per cent by the end of the year. He said: “Customers have already been hit by a double whammy of price rises last year followed by the long winter which pushed up energy usage. The average annual bill is expected to hit £1,495 with this extra cost. If, as we suspect, they hike prices again in the autumn, this could add another £100.”

On the question of increased direct debit payments Marc Gander, founder of the Consumer Action Group, said: “I am amazed they can just get away with it.”

He and other experts said millions of trusting customers – many still in credit – will hand over larger monthly payments without realising they are entitled to refuse changes to their direct debits.

The direct debit increase comes just days after British Gas vowed to use profits from increased winter usage to halt price rises “for as long as possible”.

Now it says the increase is necessary to cover the extra heating costs built up by customers over an unusually extended period of cold weather.

By making higher payments in the summer, when usage is lower, customers can avoid bigger bills at the end of the year.

A British Gas spokesman said customers could use an online tool to control their payment plans, helping them to avoid “the inconvenience of underpayment”. Energy firms say they deal with customers on a “case by case” basis but increased energy use means higher payments are inevitable.

SSE said it was “duty-bound” to review customer accounts to make sure they were not in debt and offer to adjust regular payments.

Nick McHugh, spokesman for npower, said: “Ultimately we want to achieve a £0 balance at the end of the year.

“It has been an exceptionally cold and long winter so it is going to throw the calculations out.”

Age UK director general Michelle Mitchell warned that struggling pensioners could be faced with cutting back on heating or how much they spend on food, or both, increasing their risk of illness.

This week Energy Secretary Ed Davey said people needed to be “cushioned” against rising global energy prices. He said the Government’s energy saving policies had seen the average household bill fall by five per cent. “The bills by 2020 will be 11 per cent less than they otherwise would have been if we hadn’t had our policies,” he said.